Members of the c-erbB (erbB) family of receptor tyrosine kinase genes, including epidermal growth factor receptor c-erbB1 (EGFr, HER1), c-erbB2 (HER2, neu, p185), c-erbB-3 (HER3), and c-erbB-4 (HER4), are known to be oncogenes that encode cell surface receptor proteins. The receptors, under some circumstances, display abnormal kinase activities that contribute to cell proliferation and transformation.
ErbB family receptor tyrosine kinases (RTKs) form homodimeric, heterodimeric, or perhaps oligomeric complexes that are catalytically active and, thereby, couple extracellular signals with alterations of cellular growth and differentiation status. Their ligands and subsequent receptor-mediated signaling have been implicated in survival, proliferation and differentiation in a variety of cell types (reviewed in Dougall et al. 1994; O'Rourke, et al. 1997; Pinkas-Kramarski, et al. 1997; Tzahar and Yarden 1998).
All members of the erbB family share structural features, including an extracellular ligand-binding domain that contains four subdomains, including two cysteine-rich subdomains, a single amphipathic transmembrane domain, and an intracellular kinase domain. The kinase domain shows the highest degree of amino acid sequence similarity (about 80%) among members of this family.
Overexpression of erbB receptors has been found in many types of human cancer, raising the possibility that receptor-linked therapies may be useful as cancer management strategies. EGFr (erbB1) is the most extensively studied member in this family. The EGFr gene is amplified and rearranged in many human brain tumors of glial origin and in some cell lines. Ullrich et al, has found the gene for the EGFr cellular analogue of the avian vital oncogene v-erb-B. (Ullrich et al, Nature, Vol. 309, pp. 418-425, 1984). The EGFr receptor is a transmembrane glycoprotein of about 170 kDa (Cohen, J. Biol. Chem., Vol. 258, pp. 1523-1531, 1982). Overexpression of the EGFr has been found in a variety of tumors, including bladder, esophagus, lung, glioblastoma and breast. In breast cancers, over 40% of the tumors are EGFr positive, and EGFr levels negatively correlate with steroid receptor (estrogen receptor and progesterone receptor) levels. The EGF-receptor exists in two kinetic forms (low affinity and high-affinity receptors) that may be inter-convertible. (Fernandez-Pol, Biol. Chem., Vol. 260, pp 5003-5011, 1985.) Expression of EGF-receptors has been implicated in the progression of tumor growth. In addition, an association has been detected between late stages of melanoma development and extra copies of the chromosome carrying the EGFr gene. (Koprowski et al., Somatic Cell and Molecular Genetics, Vol. 11, pp. 297-302, 1985.)
A variety of strategies have also been developed for targeting the erbB1 receptor including monoclonal antibodies, ligand-linked immunotoxins, tyrosine kinase inhibitors, and antisense approaches. (Zhang et al., 2000.) Of all the members of the erbB family, erbB2 is the most correlated to breast cancer, ovarian cancer and pancreatic cancer. Initially identified in rat neuroglioblastomas induced by a carcinogen ethylnitrosourea, neu (also known as her2/erbB2) is a proto-oncogene encoding a 185 kDa receptor-tyrosine-kinase which is highly homologous with, but distinct from, EGFr. The translation product of the erbB-2 oncogene is p185, a transmembrane glycoprotein having tyrosine kinase activity and a molecular weight of about 185,000 daltons as determined by carrying out electrophoresis on the glycoprotein and comparing its movement with marker proteins of known molecular weight. Experiments have shown that p185 forms homodimers with other p185 molecules or heterodimers with epidermal growth factor receptor EGFR (erbB1) and that these dimers exhibit elevated tyrosine kinase activity, which brings about the transformed phenotype in cells having such dimers.
Amplification of the erbB2 gene, the human homologue of neu, and subsequent overexpression of the polypeptide product p185 has been identified in 25-30% of primary breast and ovarian cancers, although no oncogenic point mutation has been detected in erbB2 associated with human carcinomas. In murine fibroblasts NIH3T3 and NR6, overexpression of erbB2 results in transformation, indicating that oncogenic mutation is not necessary for erbB2. Previous work has shown that overexpression of erbB2/neu can lead to oligomers which have enhanced kinase activity.
Overexpression of the erbB2 gene in human breast cancer is also associated with a poor prognosis and resistance to hormonal treatment and chemotherapy. Advanced stages of malignancy, characterized by large tumor size and increased number of positive lymph nodes as well as reduced survival time and decreased time to relapse, was directly correlated with an increased level of amplification of the neu gene. The neu protooncogene is expressed at low levels in normal human tissues.
c-erbB3 is expressed in a variety of normal tissues of ephithelial origin and is overexpressed in a subset of human mammary tumors. c-erbB4 (erbB3) is most predominantly expressed in several breast carcinoma cell lines and also in normal skeletal muscle, heart, pituitary, and cerebellum. The erbB3 receptor has only limited kinase activity. Overexpression of the erbB3 or erbB4 alone cannot transform NIH3T3 cells, even in the presence of ligand. It is suggested that the contribution of erbB3 and erbB4 to tumorigenicity depends on heterodimerization with the EGFr or erbB2.
Monoclonal antibodies (mAbs) and fragments from them have been used clinically for the diagnosis and treatment of many different human diseases (Dougall et al 1994, Oncogene 2109-23). The anti-tumor efficacy of mAbs not only requires specificity towards tumor antigens which show enhanced expression in neoplastic tissue, but also must demonstrate the desired biological effect, namely, the inhibition of tumor growth. U.S. Pat. No. 4,522,918, e.g., discloses a cancer treatment using monoclonal antibodies directed at surface antigens of human mammary adenocarcinoma cells.
Capone et al., JNCI 72: 673-677, (1984), investigated the relationship between antigen density and immunotherapeutic response elicited by monoclonal antibodies against solid tumors. These investigators used monoclonal antibodies specific against human breast cancer. It was found that passively administered monoclonal antibody can be effective in producing a tumor regression response against solid tumors. Tumoricidal response with monoclonal antibody appeared to be exponentially related to the density of the antigen on the cells. U.S. Pat. No. 6,252,050 describes methods for generating cross-reactive antibodies. Antibodies against p185 and methods of using such antibodies are described in U.S. Pat. Nos. 6,165,464, 5,772,997, 5,770,195, 5,725,856, 5,720,954, and 5,677,171, which are incorporated herein by reference. U.S. Pat. No. 5,705,157 describes antibodies against EGFR. U.S. Pat. No. 5,470,571 discloses a cancer treatment using monoclonal antibodies directed at the EGFr generated from the A431 carcinoma cell line. Each of the aforementioned U.S. patents is hereby incorporated herein by reference in its entirety.
In the case of receptor-dimerization, a construct containing the extracellular domain plus the transmembrane domain of p185 was able to initiate the p185-EGFr dimerization (Qian et al, PNAS 91, 1500, 1994). Later, an alternative transcript product of p185 with only subdomain I and II was found to be able to dimerize with p185 (Doherty et al. PNAS 1999, 96, 10869).
An approach for disabling receptor activity is to target protein-protein interactions involved in receptor functioning. Since protein-protein interactions play a key role in various mechanisms of cellular growth and differentiation, and viral replication, inhibition of these interactions is a promising novel approach for rational drug design against a wide number of cellular and viral targets (Zutshi et al., Curr Opin Chem Biol 1998, 2, 62-66; Peczuh et al., Chem. Rev. 2000, 100, 2479-2494). Binding of polypeptide hormones, growth factors or cytokines to cell-surface receptors activates dimerization (oligomerization) of the receptors which leads to the signal transduction to the interior of the cell (Heldin, Cell 1995, 80, 213-223). While most of the receptor inhibitors developed to date have been focused on the blockade of receptor-ligand or enzyme-substrate interactions, repression of receptor-receptor interactions that accompany oligomerization also represents an important objective for disabling receptor functioning.
Although ligand-induced homo- and heterodimerization of the full-length native erbB receptors has been established and well documented, experimental data on self-associations of the extracellular domains of these receptors is somewhat contradictory. In analytical ultra centrifugation and MALLS studies, ligand-induced homodimerization has been demonstrated for erbB1 and erbB4 (Ferguson et al., EMBO J 2000, 19, 4632-4643). However, no homo-oligomerization could be observed for the erbB3 receptor and the only erbB receptor combinations that produced heterodimers in the presence of HRGβ1 were erbB2/erbB4 and to a smaller extent erbB2/erbB3. In contrast, both erbB3 homodimerization and erbB3/erbB2 heterodimerization have been reported for the ectodomains, but these effects could only be observed when ectodomains of the receptors were anchored to the membrane (Tzahar et al., EMBO J 1997, 16, 4938-4950). Landgraf and Eisenberg have reported ligand-independent self-association of erbB3 ectodomains that could be disrupted by HRGβ1 (Landgraf et al., Biochemistry 2000, 39, 8503-8511). Both monomeric and oligomeric forms of erbB3 were detected in the presence of HRGβ1 by size-exclusion chromatography. Addition of the ligand produced a shift toward a low-molecular mass species.
The present inventors have identified distinct extracellular subdomains of erbB2 that are involved in heterodimerization with erbB1 (Kumagai et al, Proc Natl Acad Sci USA 2001, 98, 5526-5531). Peptidomimetics against subdomain IV alter the heteromeric signaling and transforming activities induced by EGF after associating with EGFR. Peptidometics and antibodies that target subdomain IV are therefore useful as therapeutic agents against erbB-expressing tumors.